clang 3.2 fails on std::atomic -- a libc++ issue?

Question

I try to compile the simple code

#include <atomic> int bar = 0; void foo(std::atomic<int>&flag) { bar = flag; }

with clang++ 3.2 (downloaded as llvm 3.2 from llvm.org; on mac os.x 10.8.3 this fails with the error

/> clang++ -std=c++11 -stdlib=libc++ -O3 -march=native -c test.cc

In file included from test.cc:1:

/usr/include/c++/v1/atomic:576:17: error: first argument to atomic operation must be a pointer to non-const _Atomic type ('const _Atomic(int) *' invalid)
{return __c11_atomic_load(&__a_, __m);} ^ ~~~~~ 
/usr/include/c++/v1/atomic:580:53: note: in instantiation of member function 'std::_1::_atomic_base::load' requested here
operator _Tp() const _NOEXCEPT {return load();} ^ 
test.cc:5:9: note: in instantiation of member function 'std::_1::_atomic_base::operator int' requested here
bar = done; 

When I use /usr/bin/clang++ instead (which comes with the OS or Xcode) it compiles just fine. The libc++ is that at /usr/lib/c++/v1 in both cases.

What am I missing? Is there another libc++ that comes with llvm 3.2 but which I'm missing? (I cannot find anything in the clang3.2 tree).

It rather seems like a library issue (spurious const) here. And no, libc++ comes within the LLVM umbrella so you should have the right one. — Matthieu M.
– Matthieu M., Commented Apr 25, 2013 at 14:59
@MatthieuM. I don't understand. the libc++ at /usr/include/c++/v1 did not come with the llvm3.2 download, but with the OS. Yet xcode seems to have its own version (see answer). so what do you mean with "umbrella" — Walter
– Walter, Commented Apr 25, 2013 at 17:13
LLVM is an open-source project with a (relatively) clear goal, the LLVM umbrella refers to projects related to LLVM; mostly those projects are hosted within the LLVM SVN server. Clang, libc++ and lldb can be thought of as being hosted by LLVM for example. So, that being said, you might have a new LLVM and be using NOT the libc++ that is adapted for it but instead another libc++ lying around somewhere on your machine. — Matthieu M.
– Matthieu M., Commented Apr 25, 2013 at 17:34

Howard Hinnant · Accepted Answer · 2013-04-25 15:11:28Z

1

Xcode now bundles libc++ within the Xcode.app directory. You can inspect this directory by control-clicking Xcode.app and choose "Show Package Contents".

answered Apr 25, 2013 at 15:11

Howard Hinnant

225k55 gold badges493 silver badges624 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Walter Over a year ago

There is indeed another libc++ at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/c++/v1/ (strange directory name with Toolchains) and its atomic differs by having __a_ declared as mutable. And this solves the problem. What I still don't get, is why there are these two different versions on my laptop. Are there also different versions of the abi?

Howard Hinnant Over a year ago

Xcode changed the location of libc++, from /usr/include to internal. Likely the installer left /usr/include instead of deleting it. The same abi, __1, is still current.

Collectives™ on Stack Overflow

clang 3.2 fails on std::atomic -- a libc++ issue?

1 Answer 1

2 Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Related